Automotive heating, ventilation and air conditioning (HVAC) systems utilize a large, hollow housing that contains various heat exchangers, blowers, outlets and rotatable valve doors that direct air flow to and through the various other components and features, depending upon their rotated position. The majority of a typical flapper type valve door, the paddle like door itself and its rotating shaft, is contained within the housing. The end of the shaft, however, extends outside the housing outer wall so as to be accessible to power actuators that rotate the shaft and door to its various positions. The outer end of the shaft is attached to a lever, the end or ends of which can be pushed or pulled by the actuator to rotate the shaft. The door has a neutral position to which it is automatically and passively returned by a spring. Therefore, the actuator need only release the lever to allow the door to spring return to a repeatable, defined starting position. However, because of relative tolerance stack ups among the various structural features that cooperate with the spring to create the passive return action, the door is sometimes subject to a slight rotational play or rattle in its neutral position.
Typically, the return spring is a coil type spring with a cylindrical body fitted over the end of the shaft and a pair of spring fingers that extend out therefrom. The spring fingers are arranged so as to be continually forcefully biased toward one another, and will pinch inwardly and tightly against any intervening structure. This inward pinching action is used to pull a pair of first opposed stop edges on the shaft into substantial parallel alignment with a pair of second opposed stop edges on the housing. So long as the two pairs of edges can in fact be moved into an aligned, parallel relation, then the spring fingers can closely, tightly contact all four edges, and the door will be rattle free in its neutral position. However, because of tolerance stack ups, a condition may occur where one spring finger can rest solidly against one pair of stop edges, but will not touch one edge of the other pair of edges. This leaves the door vulnerable to play and rattle.